As Kim stepped over the military demarcation line to enter South Korea — a first for a North Korean leader — he said the line was "actually too easy to get over" but noted that "it took us 11 years to get here."

The two leaders discussed a visit to North Korea for Moon, though Kim said such a trip might be uncomfortable for Moon because his country's transport system was not as advanced as the one in South Korea, the AP reported.

Moon replied that North Koreans would be able to enjoy the South's high-speed trains if the two countries had warmer relations and connected their rail networks, according to the AP.

Friday wasn't the first time Kim joked about interrupting Moon's sleep.

When South Korean officials visited Pyongyang earlier this year, Kim jokingly said he "decided today" to freeze missile tests "so he will not lose sleep anymore," CNN reported, citing a South Korean presidential official.